J. Kosny*, E. Kossecka**, A. Desjarlais*, and J. Christian*
Today, most of the U.S. residential buildings are being constructed using light weight wood-framed technologies, however several modern, massive building envelope technologies (masonry and concrete systems) are gaining acceptance of North American builders as well. All U.S. thermal building standards including ASHRAE 90.1 and 90.2 and Model Energy Code are linked to the steady-state clear wall R-value. This is coming from the fact that in lightweight houses dynamic responses of building envelope components (and their energy consequences) are very insignificant. That is why U.S. thermal building standards have separate requirements for high mass walls.
Very often, only steady-state R-value is used as a measure of the steady-state thermal performance of the wall. This value does not reflect the dynamic thermal performance of massive building envelope systems. Proper application of thermal mass in buildings can be one of the most effective ways of reducing building heating and cooling loads. However, these systems require a usage of dynamic thermal performance analysis.
Dynamic thermal performance of a series of wall assemblies is analyzed in this work. Results should enable an approximate dynamic thermal performance evaluation for most popular massive walls. Also, some complex structures are analyzed. Normally, complex three-dimensional building envelope components cannot be accurately simulated using one-dimensional computer models like DOE-2 or BLAST. Typically, thermal modelers have to use simplified one-dimensional descriptions of complex walls. These simplifications may significantly reduce the accuracy of computer modeling. The application of a newly developed equivalent wall theory enabled accurate whole building dynamic energy analysis for complex three-dimensional wall material configurations.
A new measure of the wall thermal dynamic performance is proposed in this paper - Dynamic Benefit for Massive Systems (DBMS). The thermal mass benefit is a function of the material configuration and climate conditions. To enable wall performance comparisons, the “R-value Equivalent for Massive Systems” is used. The R-value equivalents for massive walls are obtained by comparison of the thermal performance of the massive walls and light-weight wood frame walls.
KEY WORDS: energy, heat transfer, thermal resistance, calculation procedure, walls.
|*)||Oak Ridge National Laboratory|
|Bldg. 3247, M.S. 6070|
|Oak Ridge, TN 37831-6070, U.S.A.|
|**)||Institute of Fundamental Technological Research|
|Polish Academy of Sciences|
|Swistokrzyska 21, 00 049 Warsaw, Poland|
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Updated August 9, 2001 by Diane McKnight